Structural and Dynamical Properties of the Water Molecules Confined in Dense Clay Sediments: a Study Combining ²H NMR Spectroscopy and Multiscale Numerical Modeling

Abstract

2H NMR spectroscopy was used to detect the influence of confinement on the structural and dynamical properties of water molecules adsorbed in the interlamellar space of a natural clay (Montmorillonite) within partially hydrated self-supporting films. Multiscale numerical modeling (Monte Carlo simulations, molecular dynamics, and Brownian dynamics) was used to quantify the importance of the various relaxation mechanisms likely to be responsible for the NMR relaxation of the water molecules within such complex environment. Because of the significant fraction of iron present in these natural clays, the large value of the transverse relaxation rate measured for the confined water molecules is compatible with a dominant paramagnetic coupling modulated by the long-range diffusion of water molecules. Finally, the angular variation of the apparent relaxation rate can be used to extract the distribution of the directors of the clay lamellae within the self-supporting film.